Over the recent years, spread spectrum data communication systems have been developed in which information or data is communicated using a frequency range that greatly exceeds that of the information-bearing signal. Spread spectrum data communications utilizes a modulation technique which initiates data communication signals over a wide bandwidth in a manner so that the data communication signals are relatively immune to large amounts of noise or other channel disturbances within that wide bandwidth. Other characteristics of a spread spectrum data communications systems, for example, can include multiple access capability, multi-path operating modes, and secure communications.
Some spread spectrum data communications networks or systems utilize technology wherein a signal burst known as a "chirp" is transmitted across a data communications channel. Chirps can be sent asynchronously, or at synchronous intervals, including as concatenated chirps. Each chirp has energy spread across a frequency range. The frequency spread, for example, can be achieved by frequency sweeping or by methods of direct sequence coding. Data modulation of a chirp stream can be accomplished by means such as phase reversal modulation ("PRM") of the chirps or reversal of the frequency sequence of the chirp. A transversal filter in a spread spectrum receiver can be matched to the chirp or expected chirps thereby enabling individual chirps to be detected even on noisy network media such as radio frequency ("RF") carriers.
The data for transmission using a spread spectrum modulation technique is generally formed or grouped as packets. The breaking up of a large block of data into or so as to form small "packets" is a common technique in communications to insure that error free communications can take place even with interruptions. If an RF medium, for example, is corrupted intermittently, a large block of data will never make it through the medium without errors. Each of the small packets conventionally has some error detection bits added so that if an error is detected, a retransmission of the small packet that was corrupted will not unduly burden the network. The packet communication technique can be used to provide short control packets that check to see if the medium is clear, the other end is ready to receive, and to request retransmission if a packet did not get through correctly.
Examples of this spread spectrum data communications technology can be seen in U.S. Pat. No. 5,090,024 by Vander Mey et al. titled "Spread Spectrum Communications System For Networks," U.S. Pat. No. 5,263,046 by Vander Mey titled "Spread Spectrum Chirp Communications With Sharply Defined Bandwidth," and U.S. Pat. No. 5,278,862 by Vander Mey titled "Timing For Spread Spectrum Communication Across Noisy Media" which each include a common co-inventor and the same assignee of the present application.
In a radio frequency ("RF") data communications network, such as for office or home automation, utility data communications, or other network data communications, a plurality of transmitters and receivers communicate with each other over a network RF medium. In some of these networks, contention resolution and/or collision detection strategies are implemented to resolve situations in which two or more transmitters simultaneously require use of the network medium. An example of such a contention resolution and/or collision detection spread spectrum strategy can be seen in U.S. Pat. No. 5,359,625 by Vander Mey et al. titled "Spread Spectrum Communication System Particularly-Suited For RF Network Communication" also which includes a common co-inventor and the same assignee of the present application.
Nevertheless, despite the advantages of spread spectrum technology, interferences which are unpredictable and changing in time can continue to occur across channels. These interferences particularly become troublesome in networks where a plurality of transmitters and a plurality of receivers communicate with each other across a data communications channel and are even more troublesome in networks using carrier sense multiple access ("CSMA") and collision detection and collision resolution ("CDCR") technology which often involves simultaneous attempts to access a data communications channel by the plurality of transmitters and receivers at fast or high speeds. The CSMA/CDCR spread spectrum type data communication networks can become quite complex when attempting to address contention resolution and/or collision detection problems which often involve finding an available, clear, or best carrier frequency almost instantly for transmitting data communications thereacross. Accordingly, a continued need exists for a more robust spread spectrum data communication apparatus or system which overcomes these problems associated with data communication channel interferences which can be unpredictable and changing in time on these somewhat complex RF data communications networks.